Semiconductor package with recessed leadframe and a recessed leadframe

ABSTRACT

A semiconductor package is provided that includes a flat leadframe having front and rear faces. The leadframe includes a central platform and elongate electrical connection leads distributed around this platform. Electrical connection wires connect the chip to the front face of the leads, and encapsulation means encapsulates the chip such that the rear face of the leadframe is visible. The electrical connection leads include an inner end part and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, and the inner and outer end parts are connected by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess. The electrical connection wires are connected to the leads on the front face of their inner end part.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims priority from prior French Patent Application No. 01-07185, filed May 31, 2001, the entire disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to semiconductor packages, and more specifically to a semiconductor package having a recessed leadframe.

[0004] 2. Description of Related Art

[0005] One type of conventional semiconductor package has a leadframe made of an electrically conductive material. The leadframe includes a platform on the front face of which an integrated circuit chip is fastened and peripheral leads, the front faces of which are connected to the chip by electrical connection wires. This assembly is encapsulated, for example, in a thermosetting resin, in such a way that the rear face of the leadframe is visible so that the rear faces of the leads can be connected to the outside.

[0006] When it is desired to fasten a chip of small dimensions to the platform of the leadframe, it is necessary to provide electrical connection wires of increased length. This increase in the length of the electrical connection wires results in an increase in parasitic electrical resistance. To limit this parasitic electrical resistance, provision may be made to reduce the area of the platform and to extend the electrical connection leads inwards. However, such an arrangement causes difficulties in anchoring the electrical connection leads in the encapsulating resin and does not ensure that the rear faces of the leads have a small boundary, on which rear faces the external electrical connections will subsequently be made.

SUMMARY OF THE INVENTION

[0007] In view of these drawbacks, it is an object of the present invention to provide a semiconductor package and an electrical connection leadframe that allow the above-mentioned drawbacks to be limited.

[0008] One embodiment of the present invention provides a semiconductor package that includes a flat leadframe, an integrated circuit chip, electrical connection wires, and encapsulation means. The flat leadframe is made of an electrically conductive material. The leadframe includes a central platform and elongate electrical connection leads distributed around the platform. Each of the electrical connection leads has an inner end located on the side towards the chip and an outer end. The integrated circuit chip is fastened to the front face of the platform, and each of the electrical connection wires connects the integrated circuit chip to the front face of one of the electrical connection leads. The encapsulation means encapsulates the integrated circuit chip such that the rear face of the leadframe is visible. Additionally, at least one of the electrical connection leads includes an inner end part and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, the inner and outer end parts are connected by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess, and one of the electrical connection wires is connected to the at least one electrical connection lead on the front face of the inner end part of the at least one electrical connection lead.

[0009] Another embodiment of the present invention provides a flat leadframe made of an electrically conductive material. The leadframe includes a central platform and elongate electrical connection leads distributed around the platform. Each of the electrical connection leads has an inner end located on the side towards the chip and an outer end. At least one of the electrical connection leads includes an inner end part and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, and the inner and outer end parts are connected by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess.

[0010] Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows a cross section through a semiconductor package according to a preferred embodiment of the present invention;

[0012]FIG. 2 shows a rear view of the semiconductor package of FIG. 1;

[0013]FIG. 3 shows a partial rear view of the leadframe of the semiconductor package of FIG. 1;

[0014]FIG. 4 shows a cross section through several semiconductor packages corresponding to the semiconductor package of FIG. 1 at point during manufacturing;

[0015]FIG. 5 shows a cross section through several semiconductor packages corresponding to the semiconductor package of FIG. 1 at another point during manufacturing; and

[0016]FIG. 6 shows a cross section through a semiconductor package according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] Preferred embodiments of the present invention will be described in detail hereinbelow with reference to the attached drawings.

[0018] Preferred embodiments of the present invention provide a semiconductor package which comprises a flat leadframe made of an electrically conductive material having a front face and a rear face. The leadframe includes a central platform and elongate electrical connection leads distributed around this platform and has an inner end located on the side towards the chip and an outer end. An integrated circuit chip is fastened to the front face of the platform, electrical connection wires connect the chip to the front face of the leads, and encapsulation means is provided such that the rear face of the leadframe is visible.

[0019] Further, the electrical connection leads include an inner end part and an outer end part, the rear faces of which lie in the plane of the rear face of the leadframe. The end parts are connected by a branch, the rear face of which is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess, and the electrical connection wires are connected to the leads on the front face of their inner end part.

[0020] Preferably, the encapsulation means is an encapsulating material which extends from the rear face of the leadframe, at least between the leads and between these leads and the platform. According to one embodiment, the leads include a passage through which the encapsulating material extends.

[0021] According to another embodiment, the encapsulating material constitutes, in front of the leadframe, a block in which the chip and the electrical connection wires are embedded. According to yet another embodiment of the present invention, the encapsulating material constitutes, in front of the leadframe, a protruding ring extending outside the region where the electrical wires are bonded to the inner end parts of the leads and it includes a plate, the periphery of which is fastened to the front part of the ring so as to form a cavity between this plate and the leadframe. In embodiments of the present invention, the leads and the platform preferably have, over at least part of the periphery of their rear faces, chamfered or indented edges.

[0022] The present invention also provides a flat leadframe made of an electrically conductive material having a front face and a rear face. The leadframe includes a central platform and elongate leads distributed around this platform and has an inner end located on the side towards the chip and an outer end. Further, the electrical connection leads include an inner end part and an outer end part, the rear faces of which lie in the plane of the rear face of the leadframe, which end parts are connected by a branch, the rear face of which is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess. Preferably, the leads and the platform have, over at least part of the periphery of their rear faces, chamfered or indented edges. According to one embodiment, the branches of the leads have through-passages or through-holes.

[0023] Exemplary embodiments of the present invention will now be described in detail with reference to FIGS. 1-6. FIGS. 1 to 3 show a semiconductor package 1 which includes a flat leadframe 2 made of an electrically conductive material (for example, a metal) The leadframe has, in its central part, a square platform 3 and a multiplicity of elongate electrical connection leads 4 which are distributed around the platform.

[0024] These elongate electrical connection leads 4 are at a certain distance apart and are placed at a certain distance from the platform 3 so as to have an inner end 4 a located on the side towards the platform 3 and an outer end 4 b. The inner ends 4 a lie on a square located at a certain distance from the periphery of the platform 3 and the outer ends 4 b lie on an outer square.

[0025] The electrical connection leads 4 have, respectively, an inner end part 5 located on the side towards the platform 3 or adjacent to their inner end 4 a, an outer end part 6 at a certain distance from their inner parts 5 and adjacent to their outer end 4 b, and a branch 7 which connects their inner end part 5 to their outer end part 6.

[0026] The inner end parts 5 and the outer end parts 6 of the electrical connection leads 4 have rear faces 5 a and 6 a, respectively, which lie in the rear plane 2 a of the leadframe 2, and the branches 7 have rear faces 7 a set back with respect to the rear plane 2 a of the leadframe 2 so as to form rear recesses 8. The rear face 3 a of the platform 3 also lies in the rear plane 2 a of the leadframe 2. The platform 3 and the outer parts 6 of the electrical connection leads 4 have, around the periphery of their rear faces lying in the rear plane 2 a of the leadframe 2, chamfered or indented edges 9 and 10.

[0027] The semiconductor package 1 also includes an integrated circuit chip 11, the rear face of which is fastened to the front face 3 b of the platform 3 of the leadframe 2, and electrical connection wires 12. One end of the electrical connection wires 12 is bonded to pads 13 on the front face of the chip 11, and the other ends of the wires are bonded to the front face 5 b of the inner parts 5 of the electrical connection leads 4.

[0028] The semiconductor package 1 furthermore includes an encapsulation block 14 made of an encapsulating material (for example, a thermosetting resin). This encapsulation block 14 defines a parallelepiped which lies in front of the rear face 2 a of the leadframe 2 so as to embed this leadframe 2, the chip 11, and the electrical connection wires 12, in such a way that the rear face 3 a of the platform 3 and the rear faces 5 a and 6 a of the inner and outer parts 5 and 6 of the electrical connection leads 4 are apparent or visible.

[0029] As a result, the encapsulation block fills the spaces separating the platform 3 from the electrical connection leads 4, the spaces between the electrical connection leads 4, the rear recesses 8 of the electrical connection leads 4 and the chamfered or indented edges 9 and 10 of the platform 3 and of the electrical connection leads 4 in such a way that the leadframe 2 is held in place or anchored firmly. Thus, the rear faces 6 a of the outer parts 6 of the electrical connection leads 4 of the leadframe 2 are of small size and can advantageously be used to make the external electrical connections of the semiconductor package 1.

[0030]FIGS. 3 and 4 show a metal plate 15 which includes a multiplicity of regions 16 corresponding to the leadframe 2 and connected together by strips 17. The rear face 15 a of the plate 15 is fastened to a flat surface 18 of a support 19 by an adhesive tape 20, in such a way that the rear faces 3 a of the platforms 3 and the rear faces 5 a and 6 a of the inner and outer parts 5 and 6 of the electrical connection leads 4 of the various leadframes 2 formed in the regions 16 bear on the surface 18 of the support 19 via the adhesive tape 20.

[0031] With the plate 15 thus installed and held in place, it is then possible to fasten the various chips 11 to the various platforms 3 and bond the ends of the various electrical connection wires 12, without the platforms 3 and the inner parts 5 of the electrical connection leads moving.

[0032] Thereafter, as shown in FIG. 5, it is possible to place the leadframe 15 provided with the various chips 11 and with the various electrical connection wires 12 into the cavity 21 of an injection mold 22, by fastening the rear face 15 a against a surface 23 of the cavity 21, again by using an adhesive tape 24. Next, an encapsulating material is injected into the cavity 21 of the mold 22, which fills this cavity up to the rear face 15 a of the leadframe 15. After demolding, the molded block can be sawn up, removing the strips 17 so as to obtain a multiplicity of semiconductor packages 1 as described above and corresponding respectively to the various regions 16 of the plate 15.

[0033]FIG. 6 shows a semiconductor package according to another embodiment of the present invention. As shown, the semiconductor package 25 includes, like the semiconductor package 1 of FIG. 1, a leadframe 2, an integrated circuit chip 11, and electrical connection wires 12. The branches 7 of the electrical connection leads 4 furthermore have through-passages 26.

[0034] The semiconductor package 25 of FIG. 6 differs from the semiconductor package 1 of FIG. 1 by the fact that it has an encapsulation block 27 made of an encapsulating material which forms a protruding ring 28 lying in front of the front face of the leadframe 2, around and at a certain distance from the regions where the electrical connection wires 12 are bonded to the front faces 5 b of the inner parts 5 of the electrical connection leads 4 and of the filling parts 29.

[0035] The encapsulation block 27 made of an encapsulating material also fills, in the thickness of the leadframe 2, the spaces separating the electrical connection leads 4 from the platform 3, the spaces separating the electrical connection leads, the rear recesses 8 of the electrical connection leads and the through-holes 26 in order to connect the material filling the recesses 8 and the ring 28. The semiconductor package 25 furthermore includes a front encapsulation plate 30, the periphery of which is fastened to a front face 31 of the ring 28 by means of an adhesive, so as to define a cavity 32 containing the chip 11 and the electrical connection wires 12.

[0036] To fabricate the semiconductor package 25 of FIG. 6, the encapsulation block 27 is first produced on the leadframe 2. Next, the chip 11 is fastened and the ends of the electrical connection wires 12 are bonded, as described above. Then, the encapsulation plate 30 is fitted.

[0037] Of course, it is also possible to fit the leadframe 15 described with reference to FIG. 4, to produce in a single molding operation encapsulation blocks 25 on the various regions 16, to fasten chips 11 to the various platforms 3, to bond the electrical connection wires 12 to the various chips 11 and the inner parts 5 of the various electrical connection leads 4, respectively, to fasten various plates 30 to the various rings 28 and, then, to cut the plate 15 so as to remove the strips 17. In this way, various semiconductor packages 25 corresponding to the various regions 16 are obtained.

[0038] While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the present invention. Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Furthermore, an embodiment of the present invention may not include all of the features described above. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims. 

What is claimed is:
 1. A semiconductor package comprising: a flat leadframe made of an electrically conductive material, the leadframe having a front face and a rear face, the leadframe including a central platform and a plurality of elongate electrical connection leads distributed around the platform, each of the electrical connection leads having an inner end located on the side towards the chip and an outer end; an integrated circuit chip fastened to the front face of the platform; a plurality of electrical connection wires, each of the electrical connection wires connecting the integrated circuit chip to the front face of one of the electrical connection leads; and encapsulation means encapsulating the integrated circuit chip such that the rear face of the leadframe is visible, wherein at least one of the electrical connection leads includes an inner end part and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, the inner and outer end parts are connected by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess, and one of the electrical connection wires is connected to the at least one electrical connection lead on the front face of the inner end part of the at least one electrical connection lead.
 2. The semiconductor package according to claim 1, wherein the encapsulation means includes an encapsulating material that extends from the rear face of the leadframe, at least between the leads and between the leads and the platform.
 3. The semiconductor package according to claim 2, wherein the at least one electrical connection lead includes a passage or hole through which the encapsulating material extends.
 4. The semiconductor package according to claim 2, wherein the encapsulating material forms a block in front of the leadframe in which the chip and the electrical connection wires are embedded.
 5. The semiconductor package according to claim 2, wherein the encapsulating material forms a protruding ring in front of the leadframe, the ring extending outside the region where the electrical connection wires are bonded to the inner end parts of the leads.
 6. The semiconductor package according to claim 5, wherein the encapsulation means further includes a plate whose periphery is fastened to the front part of the ring so as to form a cavity between the plate and the leadframe.
 7. The semiconductor package according to claim 1, wherein the leads and the platform have chamfered or indented edges over at least part of the periphery of their rear faces.
 8. A flat leadframe made of an electrically conductive material, the leadframe having a front face and a rear face, the leadframe comprising: a central platform; and elongate electrical connection leads distributed around the platform, each of the electrical connection leads having an inner end located on the side towards the chip and an outer end, wherein at least one of the electrical connection leads includes an inner end part and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, and the inner and outer end parts are connected by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess
 9. The leadframe according to claim 8, wherein the leads and the platform have chamfered or indented edges over at least part of the periphery of their rear faces.
 10. The leadframe according to claim 8, wherein the branch of the at least one of the electrical connection lead has a through-passage or through-hole.
 11. A method for packaging an integrated circuit chip, the method comprising the steps of: providing a flat leadframe made of an electrically conductive material, the leadframe having a front face and a rear face, the leadframe including a central platform and a plurality of elongate electrical connection leads distributed around the platform; wherein each of the electrical connection leads includes an inner end part located on the side towards the chip and an outer end part, the rear faces of the inner and outer end parts lie in the plane of the rear face of the leadframe, and each of the inner end parts is connected to one of the outer end part by a branch whose rear face is set back with respect to the plane of the rear face of the leadframe so as to define a rear recess; fastening an integrated circuit chip to the front face of the platform; connecting a plurality of electrical connection wires between the integrated circuit chip and the front faces of the inner end parts of the electrical connection leads; and encapsulating the integrated circuit chip such that the rear face of the leadframe is visible.
 12. The method according to claim 11, wherein the encapsulation step includes the sub-step of forming an encapsulating material that extends from the rear face of the leadframe, at least between the leads and between the leads and the platform.
 13. The method according to claim 12, wherein in the encapsulation step, the encapsulating material forms a block in front of the leadframe in which the chip and the electrical connection wires are embedded.
 14. The method according to claim 12, wherein in the encapsulation step, the encapsulating material forms a protruding ring in front of the leadframe, the ring extending outside the region where the electrical connection wires are bonded to the inner end parts of the leads.
 15. The method according to claim 14, wherein the encapsulation step further includes the sub-step of fastening a plate to the front part of the ring so as to form a cavity between the plate and the leadframe. 